This invention relates to photographic cameras of the interchangeable lens type and, more particularly, to an arrangement to disable operation of the shutter release in such a camera.
In a single lens reflex camera of interchangeable lens type, the shutter is sometimes unintentionally depressed due to careless handling of the camera during exchange of lens, resulting in wasteful use of film. To avoid this problem, there has conventionally been proposed a mechanical method by which a member adapted to arrest the shutter button against depression is forced by the objective to be released as said objective is mounted on the camera body, but is restored to its arresting position as the objective is removed from the camera body. Thus, depression of the shutter button is not possible because of the depression arresting member. However, with the arresting method of such mechanical arrangement, a mechanism extending from the camera body mount to the shutter release button which governs the operation of shutter release is incorporated with members adapted for mechanical transmission and elements for automatic restoration thereof, leading to many difficulties to efficiently incorporate the members and elements into the limited space available within the camera body. Such difficulties have made practical use of the described mechanical arrangement almost impossible. A new photographic system has recently been introduced, according to which an arithmetic circuit incorporated in the camera is activated by a battery also accomodated by the camera to effect an automatic exposure control. Particularly a photographic camera of so-called automatic diaphragm control type has recently been placed on the market, with which a shutter speed is selected and preset by the operator so that the diaphragm of the individual objective actually mounted on the camera is automatically controlled in accordance with said preset shutter speed. With such camera, an electrical information transmitting system has been realized, in accordance with which the information such as the aperture values peculiar to the individual objective mounted on the camera is transmitted to the camera body through mutual contact of corresponding pairs of electric contacts arranged on portions of the objective mount and the camera body mount, respectively, to be coupled to each other. As a result, it has become easy to use said electrical information transmitting system arranged along the interface of the objective mount and the camera body mount as the method to permit and disable the operation of shutter release depending upon the presence or absence of a properly mounted objective on the camera. Namely, the most straightforward arrangement might be such that an electromagnetic release circuit adapted for direct control of the operation of shutter release is closed and opened by a switch comprising a pair of associated contacts each arranged on the objective mount and the camera body mount, respectively, so that engagement and disengagement of these contacts control the release circuit. However, such an arrangement requires separate provision of a pair of contacts exclusively for the shutter release control, which is inconvenient because of the limited area of the interface between objective and camera body.